1. Field of the Invention
This invention relates to the field of electrical transformers, and more particularly to transformers for use on printed circuit boards.
2. Background Information
A transformer ordinarily consists of wire windings around a ferromagnetic core. The windings are usually a primary winding through which electrical current is directed, and secondary windings which are electrically isolated from the primary winding. A magnetic field generated by current flow in the primary winding couples to the secondary winding, and variations in the magnetic field induce current flow in the secondary windings. The ferromagnetic core provides a low reluctance path for the magnetic field.
When used with a printed circuit board (hereinafter PC board), the transformer must be mechanically mounted to the PC board, and must also have its windings electrically coupled to conductive tracings in the PC board.
The weight of the transformer presents a problem which the mechanical mounting must overcome. Also, construction of the transformer is expensive, as it must first be assembled from a variety of separate parts, and secondly it must be mounted on the PC board.
Additionally, the turns ratio in the transformer determines the operational characteristics of the transformer, and inventory of transformers must be maintained for various turns ratio. Further, when the PC board is manufactured by a supplier, and the PC board is held in inventory by a systems manufacturer, the systems manufacturer must hold PC boards for each desired turns ratio of the transformer in its inventory, as must the supplier.
When the PC board is a power supply, such as a DC to DC power converter, then the desired characteristics of the device employing the PC board are the input voltage and the output voltage. When several output voltages are required by the systems manufacturer, then usually power at a single input voltage is supplied to each of the different power supplies, and each power supply produces power at the desired output voltage. A systems manufacturer which requires a plurality of power supplies, each delivering power at a different voltage, must maintain in inventory PC boards with a transformer for supplying power at each required voltage. Also, the vendor of the power supplies must maintain in inventory complete PC boards containing the different transformers for supplying power at the different required output voltages.
The transformer may be the only part on the PC board which is different, from output voltage to output voltage, where the transformer determines the value of the output voltage of the power supply.
There is needed a better way to couple a transformer to a PC board so that manufacturing costs are reduced, and also so that the number of parts held in inventory by a manufacturer of power supplies is reduced.